[RF] Improve Home Assistant auto discoverability (#2057)

* add '-DvalueAsATopic=true' to RF based environments
add '-DvalueAsATopic=true' to RF based environments. Required to support changes in zgatewayRF.ino for Home Assistant discoverability

* Modify gatewayRF to improve Home Assistant auto discoverability
Pass "recieved" as the type argument and switchRF[0] as the subtype argument to announceDeviceTrigger() which will cause recieved codes to be picked up by home assistant as triggers, i.e. When setting up automations in Home Assistant, selecting a `device` trigger and an OMG device will allow the user to select a code picked up during the autoDiscover window as the trigger for the automation, for example "1394004" recieved. In order to support this, the `'-DvalueAsATopic=true'` argument must be added to all environments using the RF Library

Also change getUniqueId() call to remove leading '-' which will prevent MQTT topics having '--' in them

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Co-authored-by: James Carey <james.carey@uws.ac.uk>

main/ZgatewayRF.ino

@@ -95,12 +95,14 @@ void RFtoMQTTdiscovery(uint64_t MQTTvalue) {
   String discovery_topic = String(subjectRFtoMQTT);
 #    endif
 
-  String theUniqueId = getUniqueId("-" + String(switchRF[0]), "-" + String(switchRF[1]));
+  String theUniqueId = getUniqueId(String(switchRF[0]), "-" + String(switchRF[1]));
+  String subType = String(switchRF[0]);
 
   announceDeviceTrigger(
       false,
       (char*)discovery_topic.c_str(),
-      "", "",
+      "received",
+      (char*)subType.c_str(),
       (char*)theUniqueId.c_str(),
       "", "", "", "");
 }